Evidence for a partial epithelial-mesenchymal transition
in rat auditory organ developmentNicolas JOHNEN, Marie-Emilie
Francart, Marie Cloes, Nicolas Thelen and Marc Thiry
GIGA-Neuroscience, Cell and Tissue biology Unit, Université de
Liège
Contact : [email protected]
Conclusion
Introduction
Results
An epithelial-mesenchymal transition (EMT) is a biological
process that allows a polarized epithelial cell to undergo multiple
biochemical
changes that enable it to assume a mesenchymal cell phenotype
(Kalluri and Weinberg 2009; Savagner 2010; Thiery et al. 2009).
During
this process, epithelial cells loosen cell-cell adhesion, module
their polarity and rearrange their cytoskeleton: intermediate
filaments
typically switch from cytokeratin to vimentin. They also enhance
their motility capacity. The EMT plays key roles in the formation
of the
body plan and in the differentiation of multiple tissues and
organs but it is also involved in tissue repair, tissue
homeostasis, fibrosis, and
carcinoma progression (Thiery et al. 2009) (Fig 1).
Until now, EMT has been rarely mentioned in the inner ear
organogenesis. In chick, EMT has been reported as a possible
mechanism of
semicircular canal morphogenesis (Kobayashi et al. 2008). More
recently, an in vitro study has also indicated that sensory
epithelial cells
from mouse utricle can undergo an EMT to become cells expressing
features of prosensory cells (Zhang and Hu 2011). By contrast,
EMT
has never been observed during auditory organ morphogenesis.
The auditory organ, the organ of Corti (OC), is a highly
specialized structure composed by specific cellular types. The
sensory cells are
characterized by stereocilia at their apex and are necessary for
the sound perception. These cells are supported by supporting
cells. Based
on their morphology and physiology, at least four types of
supporting cells can be identified in the OC (Fig 2): inner and
outer pillar cells,
phalangeal cell and Deiter’s cells. The inner pillar cells and
outer pillar cells combine to form the tunnel of Corti, a fluid
filled triangular
space that separates the single row of inner hair cells from the
first row of outer hair cells. The Nuel spaces are another interval
in the OC
that is situated between the outer pillar cells and the
different rows of outer hair cells and Deiters cells.
To determine whether an epithelial-mesenchymal transition may
play a role in the morphogenesis of the auditory organ, we studied
the spatial localization of several EMT markers, the
cell-cell adhesion molecules and intermediate filament
cytoskeletal proteins, in epithelium of the dorsal cochlea during
development of the rat OC from 18th embryonic day (E18) until
25th postnatal day (P25).
Partial loss of E-cadherin between the pillar
cells and between the Deiters’ cells from P8
Fig 1
Fig 2
Temporary presence of vimentin in pillar and
Deiters cells at P8-10
Intense expression of cytokeratin in
supporting cells at P10-12
A. E-Cadherin immunolabeling within the dorsal epithelium of the
cochlear duct from P8 to P16. A-D. Immunolocalization of the
E-Cadherin (red). A’-D’. Merged image with cell nuclei
stained with DAPI (blue). A’’-D’’. Visualization of the OC by
transmission detector. Bar = 10 µm
B. E-Cadherin immunolabeling of the organ of Corti at P6, P10
and P16 in transversal view projection on the XY axis. The lines
indicate the starting level for the projection on the XZ level
shown on XX’ of the OC and they are signalled below by XX’. XX’
projection of the organ of Corti on the XZ plane.
Arrowheads/Asterisks represent loss/maintaining of E-cadherin
labeling
(red), respectively. Cell nuclei are stained with DAPI (blue).
Bars = 15 µm
Vimentin immunolabeling within the dorsal epithelium of
the cochlear duct from P8 to P16.
A-D. Localization of the hair cells by using Myosin VI (red).
A’-
D’. Immunolocalization of the vimentin (green). A’’-D’’.
Merged image with cell nuclei stained with DAPI (blue). Bar
=
10 µm
Cytokeratin 8 immunolabeling within the dorsal epithelium
of the cochlear duct from P8 to P12.
A-C Localization of the supporting cells by using p27kip1
(green). A’-C’. Immunolocalization of the cytokeratin 8
(red).
A’’-C’’. Merged image with cell nuclei stained with DAPI
(blue). Bar = 10 µmAnnotations: D(1-3) Deiters’ cell, I inner
hair cell, Ip inner pillar
cell, N Nuel’s spaces, O(1-3) outer hair cell, Op outer pillar
cell, P
phalangeal cell, PX Post-natal day X, TC tunnel of Corti, and
V
spiral vessel.
A
B
Our results show a local loss of adhesion between supporting
cells of the OC from P8, an increase expression of cytokeratins in
supporting cells around P10 and a temporary
appearance of vimentin in supporting cells at P8-10. These
observations suggest that a partial epithelial-mesenchymal
transition might be involved in the remodeling of the Corti
organ
during the postnatal stages of development in rat.
